1. Field of the Invention
This invention relates generally to an alternating current power grid system and, more particularly, a method and apparatus for capturing voltage phase angle data on an alternating current power grid.
2. Description of the Background Art
In the background art it is well known that useful information about the state of an alternating current (AC) power grid can be obtained by measuring the phase angle between the voltages at different locations. In the background art, these locations are typically on the high-voltage bulk power transmission section of an AC power grid. The information obtained by such measurements can include information about power flow in complex grids, information about grid stability, and information that is useful for operating protective devices on an AC power grid. This information can be used to improve the reliability and efficiency of an AC power grid.
Typically, these angles are measured using Phasor Measurement Units (PMUs). A PMU is an electronic device that processes analog voltage waveform data at a location on the power grid in order to measure voltage phase angle at that location. PMUs are typically installed at multiple locations in order to measure the voltage phase angles between those locations. The voltage phase angle at each location is initially measured relative to a common timing reference, typically a Global Positioning System (GPS) timing reference signal. PMUs typically produce measurements at a rate between 60 measurements per second and 1 measurement per second that must immediately be sent to one or more Phasor Data Concentrators in real time for comparison to angles transmitted by other PMUs. Such a system inherently requires a high-reliability, high-bandwidth data transmission connection between the PMUs and the Phasor Data Concentrator. Due to the resource-intensive nature of such a phasor monitoring system that includes a high-reliability, high-bandwidth data transmission connection, utility companies have economically justified the use of PMUs only on the transmission system of the power grid where the flow of power has a very high economic value, but not on distribution systems or low-voltage systems where smaller amounts of power flow occur.
In recent years, it has been observed that some disruptions to the power grid have resulted in increasing instability on the power grid (i.e., greater phase angle oscillation swings between remote locations on the grid). One theory is that the growing number of small power generators (e.g., photovoltaic solar panels, home-based wind turbines, fuel cells, electric vehicle energy storage systems) on the power grid may be causing at least a portion of this increased instability, but more study is required to determine the validity of this theory.
Small power generators such as photovoltaic arrays, wind turbines, and fuel cells may sometimes be located within distribution systems or low-voltage systems of the power grid. In order to determine the effect of these generators on the stability of the AC power grid, it would be useful to obtain voltage phase angle data from locations within distribution and low-voltage systems. As discussed above, known PMUs require high-data, high-bandwidth networks to transmit voltage phase angle data, and it is economically difficult to justify the resources required to install such networks within distribution systems or low-voltage systems. Nevertheless, with the proliferation of photovoltaic solar panels, home-based wind turbines, fuel cells, and electric vehicle energy storage systems, there is an increasing need for voltage phase angle data from locations within distribution and low-voltage systems.